The closest prior art known to the applicant is of its own prior patent application published as GB2353584. This prior art document concerns blank training cartridges for a self-loading gun. The cartridges of this prior published invention expand following the detonation of its primers. The cartridge shown in this document expands rearward through a piston which has exposed portions from the cartridge's casing. Consequently, the profile of the cartridge changes following detonation as it expands in overall length. The expansion of these cartridges is particularly useful for cycling self-loading guns.
The main problems of these prior art cartridges are:    a) Unreliable feeding from a magazine;    b) Unreliable cycling of heavier calibre guns; and    c) Relatively poor ejection of spent rounds.